Someone that does not want to use SLI? Smart one!!
The Opteron 165 is a great CPU and it overclocks really well. Assuming you want to overclock it, go with the OCZ RAM. It will O/C much better than the Corsair Value RAM. Make sure you get 2 x 1GB and not just 1 2GB stick.
As for motherboard, all 3 are good choices, but I am partial to Asus. I have never had any problems with Asus products, they include eveything you would ever possibly need cable wise with their boards, and they are generally good quality. The A8N-E is agood deal at $95 (newegg).
Video card is a good choice, 7900s are sweet cards, and the GT will outperform (or come close) to the 7800GTX. PSU is fine as well.
Monitor looks like a great deal on Newegg. Don't have any experience with Hyundai, but it gets good reviews. As for hard drive, brand does not really matter, the only thing I would go for is an SATA 3.0gb/s drive with a 16MB cache. I perfer Seagate drives (mainly for the 5 year warranty) but WD is ok too.
I just (1.5 weeks ago) put together a system based on a opty 165. Im using it for a variety of things among them playing games ...
I use 2x1 selectra CL2.5 ram. Sure, not top brand, but it easily copes with 230+ FSB just by bumbing to CL3 (when running @2.493 GHz). I know you can do this alot more serious, but i settled for this at the moment since it still is a decent OC... (39%)
My point is, stay away from (too) expensive memory if your on a budget.
I also got a Sapphire x800GTO2, again far from high end, but a really good value. And since i also use a 19" LCD@1280, it provides the power for almost any game.
Case and PSU; i bought the antec p150. it comes with a 430w PSU which is really silent. actually the whole system is (except maybe from the stock HSF but its not that bad).
alltogether, a really high performing and quiet PC (yes, I know im just a fart compared to you serious OC guys).
And considering the GPU, since the res. is limiting the need for a more radical GPU at this point, I went for a "cheap" card, which i can rip out and replace with a new one without bad feelings in 6 months or so if needed...
Dont worry about ram if your motherboard has a ram divider. Overclocking the ram on an AMD system is stupid. As AMD excells due to low latency memory timings with the on chip memory controller. You OC the RAM and fatten up the timings hurting performance. Just get some good brand name PC3200 DDR RAM and your golden.
after tweaking im stable @2.8ghz with 1.45volts, you need a dfi mobo to hit 2.8ghz with a 165 because of the 9x multiplyer. I like asus mobos but they cant handle over 300fsb, thats what you need to get to 2.8ghz with a opty 165.
oh yeah, I run my memory @ 208mhz (311htt/fsb) with a 2/3 divider, on any a64/opteron the memory controler is on the cpu, so you dont need to oc the memory.
All premium boards have diveders, however the steps between the values differs. I use a A8N sli premium board. to match the increased FSB speed, the memory divider has to be lowered (you know this already). The step below 400 is 333 which is a slight overclock with my FSB.
so in the end, even if your not planning to OC the RAM, good ram with som headroom will make it easier to find a good FSB/ divider combination (and hence not having to Underclock your ram)